It is well-known in the field of eyeglass manufacture to construct eyewear, such as eyeglasses, sunglasses, goggles, etc., with resilient hinge joints between the eyeglass frame and the temple bar so that the eyeglasses fold when not in use. Resilient means acting upon the hinged joints have also been employed to hold the temple bar in a folded condition or biased to the open position, or both. The biasing has been accomplished in many ways, including the use of cams acting upon resilient members, such as metal coil springs, to achieve their purpose. There have been efforts to replace the more complicated and expensive metal coil spring structures with molded-in metal leaf springs which also employ an intermediate roller such as taught in U.S. Pat. No. 4,605,293. There is, however, heretofore not been devised an inexpensive one-piece molded cam and spring hinge joint that functions adequately.
There have also been various attempts to create eyeglass hinge joints in which the temple members are detachable from the frames at the hinge joint. The use of resilient material for the temple bars has permitted snap-over joints where jaws of the temple frames are spread apart and fitted over top and bottom pins located on the frame member half. Similarly, these corresponding structures have been reversed between the respective elements of the hinge mechanism with the same result.
Examples of this technology is disclosed in several U.S. patents. U.S. Pat. No. 4,153,347 discloses an eyeglass hinge pin having an angled surface which wedges spreadable temple jaws apart upon insertion. U.S. Pat. No. 2,210,507 discloses the use of a spreadable outer hinge element fitted around temple bar hinge pins. Insertion is made easier by rounding the ends of the pins to reduce friction and provide a wedging effect during insertion. U.S. Pat. No. 4,832,478 shows the use of a hinge assembly for an eyeglass frame in which the spreadable hinge leaves on the temple bar include ramps to guide a frame-mounted hinge pin and spread the temple bar leaves as the hinge pin is inserted. There is difficulty with these hinged joints, however, because to spread the outer hinge apart takes a great deal of force to accomplish. Thus, attachment and removal is difficult. Efforts to reduce the attachment force by providing insertion ramps or rounded pin ends can cause a joint to come apart too easily. There is therefore a need in the art for a detachable eyeglass frame/temple hinge joint which may be easily removed when desired, but which after installation provides secure attachment between the hinged parts.